Fluid transport systems are well known and used in a number of applications. For example, ink may be transported from a supply to one or more print heads in a printer and medicines may be delivered from a liquid source to a port for ejection into a patient, to name only two known applications. One method of moving fluids in these known systems is a peristaltic pump. A peristaltic pump typically includes a pair of rotors through which a delivery conduit is stationed. The rotation of the rotors under the driving force of a motor squeezes the delivery conduit in a delivery direction. As an amount of the fluid is pushed in the delivery direction, the supply continues to fill the delivery conduit so fluid is continuously pumped through the delivery conduit to the ejection port.
One issue that arises from the use of peristaltic pumps is the repetitive squeezing of the conduit. As the rotors rotate, they typically force the walls of the conduit closely together before allowing them to rebound. As the number of times that a short length of the conduit is collapsed and expanded increases, the life of the conduit is adversely impacted. One way of addressing this risk of a shortened life cycle for the conduit is to use materials for the conduit that are more resilient than those commonly used for fluid conduits, such as silicone elastomers. Unfortunately, the more resilient materials are expensive and in some applications cost competition is intense.
Other methods used in systems for delivering fluid through a conduit include the provision of a reservoir with a bladder located in the reservoir. The bladder is coupled between an inlet valve and an outlet valve. The bladder is cyclically filled with a gas to pump fluid out of the reservoir and then vented before commencement of the next cycle. Another method injects a compressed gas into an enclosed reservoir to urge fluid from the reservoir. The pressure in the enclosed reservoir is continually increased until the fluid supply in the reservoir is essentially exhausted. In response to a low level in the reservoir being sensed, the gas injection is terminated and the pressure in the reservoir is vented so the reservoir may be replenished or replaced. After replenishment or replacement, compressed gas is again introduced into the reservoir to move fluid into and through a conduit. The pumps used in these various methods to pressurize a reservoir or internal reservoir chamber, however, are generally expensive or bulky for some applications.
Solid ink or phase change ink printers, as noted above, also transport liquid ink from a reservoir to a print head. These printers conventionally use ink in a solid form, either as pellets or as ink sticks of colored cyan, yellow, magenta and black ink, that are inserted into feed channels through openings to the channels. Each of the openings may be constructed to accept sticks of only one particular configuration. Constructing the feed channel openings in this manner helps reduce the risk of an ink stick having a particular characteristic being inserted into the wrong channel. U.S. Pat. No. 5,734,402 for a Solid Ink Feed System, issued Mar. 31, 1998 to Rousseau et al.; and U.S. Pat. No. 5,861,903 for an Ink Feed System, issued Jan. 19, 1999 to Crawford et al. describe exemplary systems for delivering solid ink sticks into a phase change ink printer.
After the ink sticks are fed into their corresponding feed channels, they are urged by gravity or a mechanical actuator to a heater assembly of the printer. The heater assembly includes a heater that converts electrical energy into heat and a melt plate. The melt plate is typically formed from aluminum or other lightweight material in the shape of a plate or an open sided funnel. The heater is proximate to the melt plate to heat the melt plate to a temperature that melts an ink stick coming into contact with the melt plate. The melt plate may be tilted with respect to the solid ink channel so that as the solid ink impinging on the melt plate changes phase, it is directed to drip into the reservoir for that color. The ink stored in the reservoir continues to be heated while awaiting subsequent use.
Each reservoir of colored, liquid ink may be coupled to a print head through at least one manifold pathway. The liquid ink is pulled from the reservoir as the print head demands ink for jetting onto a receiving medium or image drum. The print head elements, which are typically piezoelectric devices, receive the liquid ink and expel the ink onto an imaging surface as a controller selectively activates the elements with a driving voltage. Specifically, the liquid ink flows from the reservoirs through manifolds to be ejected from microscopic orifices by piezoelectric elements in the print head.
As throughput rates for liquid ink print heads increase, so does the need for delivering adequate amounts of liquid ink to the print head. One problem arising from higher throughput rates is increased sensitivity to resistance and pressures in the print head flow path. Restricted ink flow can limit or decrease imaging speed. In systems having filtration systems for filtering the liquid ink between the reservoir and a print head element, the flow may also change over time and become insufficient to draw liquid ink to the print head in sufficient amounts to provide the desired print quality.
One way of addressing the issue of flow resistance is to increase the filter area. The increased filter area decreases the pressure drop required to migrate a volume of ink through the filter. Increasing the filter area, however, also increases the cost of the printer as filtration material is often expensive. Moreover, the space for a larger filter may not be available as space in the vicinity of a print head of in a phase change printer is not always readily available.
Another way of overcoming flow resistance as well as increased volume demand with fast imaging is to pressurize the liquid ink to force the ink through a restrictive flow path. One known method of pressurizing a fluid in a conduit is to use a peristaltic pump. As noted above, peristaltic pumps may adversely impact the life of the conduit. Consumers of solid ink printers are sensitive to price and the use of peristaltic pumps with more expensive conduit material may negatively impact pricing of the printers.
The other methods for pressurizing fluid in a conduit noted above also pose tradeoffs in solid ink printer manufacture. For example, inclusion of the reservoir and reservoir arrangement noted above may require extensive modification of some existing printer designs to accommodate the pump operating parameters. If the arrangement of existing components is too extensive, then other limitations may arise, such as space constraints.